Experimental Detection of Functional Properties of the Semi-Rigid Fillers
Possibility of quick fixes or need to extend life of existing thin-walled structural elements, such as pressure vessels, piping and other, workers under internal pressure media, seems promising application of pressurized protecting sleeve. Such a sleeve could consist of a divided metal housing or jacketed sleeve and curable sealing elements or curable filling materials. This solution is particularly suitable for repairing corrosion-damaged pipelines. The main problem of this technology is to select an existing filling material. Materials as fillers must meet a number of specific requirements. One of the main goals was to determine the rate of decline in the relative volume changes and the rate of pressure drop. Appropriate method was chosen using the results of strain measurement.
At a glance: Figures
Keywords: pressurized protecting sleeve, Two Component Plastic Materials, pressure vessel, volume shrinkage, semi-rigid filler, Strain Measuring
American Journal of Mechanical Engineering, 2013 1 (7),
Received October 24, 2013; Revised October 31, 2013; Accepted November 22, 2013Copyright © 2014 Science and Education Publishing. All Rights Reserved.
Cite this article:
- Sivák, Peter. "Experimental Detection of Functional Properties of the Semi-Rigid Fillers." American Journal of Mechanical Engineering 1.7 (2013): 451-456.
- Sivák, P. (2013). Experimental Detection of Functional Properties of the Semi-Rigid Fillers. American Journal of Mechanical Engineering, 1(7), 451-456.
- Sivák, Peter. "Experimental Detection of Functional Properties of the Semi-Rigid Fillers." American Journal of Mechanical Engineering 1, no. 7 (2013): 451-456.
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Solving tasks within the group, the essence of which is to increase the carrying capacity of existing thin-walled structural elements, such as pressure vessels, piping and other, workers under internal pressure media, the possibility of quick fixes or need to extend their life, when the total exchange was still ineffective, not to mention the economic losses during their closure, seems promising application of pressurized protecting sleeve . Such a sleeve could consist of a divided metal housing or jacket or sleeve and curable sealing elements or curable filling materials Figure 1.
Protecting sleeve is installed without reducing the internal pressure on damaged pipes without dismantling [3, 7]. This solution is particularly suitable for repairing corrosion-damaged pipelines . Two semi-cylindrical parts that have to be passed to the pipeline form such pressurized sleeve and they are connected to each other with screws or welded. Fronts are sealed. Cavity between the sleeve and the pipe is then filled with a suitable material so that the liquid fill has been formed the pressure which is maintained constant until it has hardened. The whole story takes place at an operating pressure in the pipeline. Pipe is then pressed by sleeve at a pressure at which hardened semi-rigid filler.
2. Filling materials2.1. Requirements for Filling Materials
The main problem of this relatively advanced technology is development of new material, respectively selection of an existing filling material . Materials as fillers must meet a number of specific and often conflicting requirements.
Here are some of them:
to prepare a larger amount of mass (150 l) in 5 minutes;
must not cause gas bubbles;
sufficiently low viscosity at least 30 minutes to fill cavities;
minimal temperature and volume changes;
completion of curing within 48 hours at ambient temperature 30° C;
sufficient tensile strength to prevent damage due to the pressure drop line;
sufficient bond strength to steel;
inertness against steel;
non-absorbability and moisture resistance;
temporal stability.2.2. Specifications of Selected Materials
In accordance with the following requirements set was examined several materials supplied by producers based on predefined criteria. Materials were based on two-component polyurethane adhesive Icema® R-series made by the H. B. Fuller GmbH Austria. Their basic characteristics are specified in the Table 1, Table 2, Table 3, Table 4.
Selected materials were first subjected to the tests for assessing the qualities essential for the processing of materials (viscosity, temperature variation and change in the free volume of curing) and tests of mechanical properties (modulus, strength and elongation). In the second step materials were subjected to the tests curing under pressure. They were aimed to determine whether at higher pressures (up to 10 MPa) occurs curing of materials and to determine changes of material properties during hardening under pressure.
3. Experiment3.1. Design of the Experiment
For this purpose, an experiment was designed as a pressurizing thin rotary-symmetric cylindrical shell (vessel), where using strain gages applied to the surface of the vessel have been identified small deformation in the circumferential and longitudinal direction in the vessel wall as response curable effect of filling in the vessel . Shape and dimensions of experimental vessels Figure 2, and Figure 3 were designed to strain gauges data were not influenced by edge effects (including addition, given the different stiffness of the walls and bottom of the container), i.e. to meet the assumptions of membrane tension. At the same time, to ensure a sufficient level of signals without causing plastic deformation , assuming a working pressure up to 10 MPa. Working pressure was applied through the lever grease gun, which transmits pressure to the cylinder filling materials. Pressure was also controlled by calibrated pressure gauge [8, 9].3.2. The Measuring Chain
During the experiment was used measuring system as shown in the Figure 4.
The main parts of the measurement chain were: the active and compensation resistive 120-ohm strain gauges (90-degree rosette) (Micro Measurements Group Vishay and Baldwin Lima Hamilton) in quarter and half-bridge circuits, the digital strain indicator Model P-3500 (Micro Measurements Group Vishay), the switch & balance unit SB-10 (Micro Measurements Group Vishay), a digital thermometer, pressure gauge and universal lever grease gun. The models P-3500 and SB-10 are portable, battery-powered high precision instruments for use with resistive strain gages and transducers, primarily intended for the experimental stress analysis (ESA).
Before measuring the vessel was filled with two components well mixed filling. Then the vessel was closed and de-aerated. Finally, the desired pressure has been developed by the lever grease gun. Changes occurring during curing were monitored using a pressure gauge and using strain gauges. During the measurement process was observed volume shrinkage of filling, which is inherent in curing materials. This shrinkage significantly decreased the pressure in the system. It was therefore necessary to gradually prolonging the intervals of repeated pressurization.3.4. Measured Data
The pressure trend and temperature of the vessel versus time is shown in the Figure 5 and Figure 6. There have been observed changes in pressure at the start of curing, which had to be periodically refreshed in order to maintain preload of pressure vessel.
The pressure trend versus temperature of the vessel is shown in the Figure 7 and Figure 8. The regression curves with the relevant equations and correlation coefficients are also attached. Using strain gages were measured principal strains in circumferential and longitudinal direction of the pressured vessel. The principal strains trend versus pressure of the vessel is shown in the Figure 9 and Figure 10.
4. Determination of the Speed of Changes
One of the main goals in this experiment was to determine the rate of decline in the relative volume changes and the rate of pressure drop. Appropriate method was chosen using the results of strain measurement, starting from the assumption, that the cavity inside cylindrical vessel will have the same shape even after loading and subsequent deformation.
The volume of the experimental vessel as cylinder is expressed (for radius r and length l) by the relationship
If all members can consider variables, then the total volume change can be determined by differentiation of equation (1) to give the total differential
and in finite increments
By using relations for relative length changes
The relative volume change is equal to
The speed of relative volume changes is equal to
in finite increments
and by using equation (8)
Similarly the speed of pressure change is equal to
Thus was obtained the time course of the decrease of the relative volume change, as illustrated in the Figure 15, Figure 16 and the time course of the decrease of the pressure, as illustrated in the Figure 17, Figure 18, and Figure 19. All dependencies are based on real-time t. The trend lines (as the power functions) with the relevant equations and correlation coefficients are also attached. It is apparent rapid decrease in size of the two observed variables during the first hours of curing and then their gradual convergence to zero.
5. Checking Condition of the Fill
After completing the measurements, each vessel was cut lengthwise and transverse to check the fill Figure 20 and Figure 21. The object of observation was mainly state and homogeneity of the fill, cavities, etc.. It has been observed complete filling of the vessel. The filling was homogeneous and bubble-free. Due to shrinkage of the filling in the upper part of the vessel was created the cavity Figure 22. This cavity was gradually filled by pressurized medium. The size of this cavity corresponds to the absolute value and relative volume changes of the fill, which was always greater than for curing under atmospheric pressure (of the order of 3.5% versus 1%).
In the event that the observed shrinkage crucially took place in the early stage of curing before solidifying material, it is possible to eliminate the negative effects of shrinkage by maintaining a constant pressure fill by pressurizing the system. This ensures that the material will also cure unable to maintain the required preload sleeve-pipeline system. This must be taken into account when designing and technological progress pressurizing the sleeve. It is necessary to ensure the replenishment of materials and maintain the desired pressure during early curing. As follows from (not listed here) comparative calculations experimental vessel with sleeves can be expected significantly less impact the shrinkage on the filling pressure drop. Similarly, it can be assumed less influence fill volume changes from temperature changes. These conclusions can be verified experimentally only for real models with sufficient similarity with the pressurized sleeves.
The materials Icema R 141/40 P and Icema R 141/70 may be based on past results considered being applicable. The material Icema R 142 Schwarz appears to be less suitable. It is critical that the manufacturer can guarantee the stability of the processing characteristics, in particular the minimum processing time at pipe about 40°C.
This work was supported by grant projects VEGA No. 1/0289/11, VEGA No. 1/1205/12 and VEGA No. 1/0937/12.
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